feat(spotify): orchestrate go-librespot backend from BotInstance (Stage 2 Task 7)

Construct one SpotifyController per bot (config.spotify + per-bot work/config
dirs under DATA_DIR, threaded via BotManager + index). resolveAndPlay now
routes spotify: sentinels through controller.ensureStarted/playTrack +
player.playPcmStream (falling back to the Stage-1 message when unavailable),
fences/pauses the sidecar on source transitions, advances via controller
"trackEnded", and delegates pause/resume/stop transport. Correction C4:
no re-attach on a spotify->spotify handoff (playPcmStream once across tracks,
no player.stop() — playPcmStream fences the prior ffmpeg internally); occupancy
auto-pause/resume + updateAutoPause + a new BotInstance.seek() (web seek route)
also delegate to the sidecar.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/index.ts

@@ -29,6 +29,7 @@ const LOG_DIR = path.join(DATA_DIR, "logs");
 const COOKIE_DIR = path.join(DATA_DIR, "cookies");
 const AVATAR_DIR = path.join(DATA_DIR, "avatars");
 const LOCAL_AUDIO_DIR = path.join(DATA_DIR, "local-audio");
+const SPOTIFY_DATA_DIR = path.join(DATA_DIR, "spotify");
 const STATIC_DIR = path.join(ROOT_DIR, "web", "dist");
 
 async function main() {
@@ -94,7 +95,8 @@ async function main() {
     CONFIG_PATH,
     localProvider,
     kugouProvider,
-    spotifyProvider
+    spotifyProvider,
+    SPOTIFY_DATA_DIR
   );
   await botManager.loadSavedBots();